Overflow coolant container cold level

Hi everyone, thought I would post this here as it applies to all 4 tech engines.
I have a 2012 speedster 150, 260 hp boat. Just ran it for the first time this weekend.
The coolant before I ran it when it was cold was up to the min line on the coolant container.
After running it a few times on Saturday then letting it sit overnight (so the engine was cool the next morning) I checked the coolant container and it was only about 1/2 inch up from the bottom of it and at least 1 inch below the minimum line where it was before.
Don't see any signs of coolant anywhere in the bilge.
Someone else told be it could be one of two things: Either when the dealership set it up they did not setup the cooling system properly (incorrect pressurization) and could have had left air bubbles in the system taking up coolant room, or there is a leak in the cooling system.
I don't think it is a leak though as the system must be pressurized for when the engine is hot the coolant level rises about 1/2 inch but is still below the minimum mark for when the engine is supposed to be cold.
Was going to haul the boat all the way back from the cottage to the dealership but decided to wait, buy some more coolant, fill the overflow to somewhere between the min and max mark for when it is cold then monitor it to see if it stays there. If it does great if not will take to dealer to have looked at.

Anyone have any experience with this before ?
Does my plan sound reasonable ?
Is there anyway I could damage anything with following my plan ?

IMO fill it back up and take it out an see. Most likely it wasn't "burped" and there were a couple of air pockets. check inside the hull for ANY coolant in the bottom and also, underneath the boat, if it's in the garage, etc. if no leaks, refill and ride, then recheck.